Field of the Invention
The present invention relates to a Vertical Takeoff and Landing (VTOL) aircraft, more particularly to a high performance VTOL aircraft for executing hovering flight, forward flight, and transitioning between the two in a stable and efficient manner.
Discussion of the Background
Vertical Takeoff and Landing (VTOL) aircraft is an aircraft can take off, hover, transition to forward flight, and land vertically. Many designs had been proposed for several years. One of the main challenges of this type of aircraft design relates to the relative placement of propulsion units and wings in order to minimize interference such as the slipstream of the propulsion units hitting the wings thus reducing their effectiveness. For example, this is the case of the U.S. Pat. No. 8,616,492. U.S. Pat. No. 8,616,492 uses six propellers that are strategically placed so that the propeller slipstream of the fans only minimally hits parts of the aircraft when in forward flight configuration. However, a large fraction of the propeller slipstream hits the wing in when the propellers are in vertical flight configuration. Another attempt to circumvent this problem is provided by U.S. Pat. No. 6,655,631. U.S. Pat. No. 6,655,631 places the propellers on structures that extend forward and backwards from the wing far enough such that the propeller slipstream does not hit the wing in hover configuration. However, since the propellers rotate in place, the propeller slipstream from the front propellers hits the rear propellers and the wing when in forward flight configuration. This could cause a significant loss in performance of the rear propellers.
Further and more recent US patent application 20120261523 places the propellers similar to that of U.S. Pat. No. 6,655,631, but the entire structure rotates maintaining the same relative position of the fans such that the propeller slipstream of one fan never hits the another fan or the wing. Unfortunately on US patent application 20120261523 the propeller slipstream from the propellers contacts the propeller supporting structures at all times. Yet another significant setback of US patent application 20120261523 is that the size of the propellers and the overall design of the aircraft are significantly constrained by the requirement that the propeller disks and wings cannot overlap when seen from a top view of the hover configuration, and also that larger diameter propellers would need longer and heavier the supporting structures.
Another proposed design comprises a more compact planform reducing size and weight as in U.S. Pat. No. 2,478,847. However, the design presented in U.S. Pat. No. 2,478,847 A suffers from two major flaws which make it unpractical. Firstly, the design uses only two propellers under the wing, which would produce an aircraft that behaves as an inverted pendulum about its pitch axis, and therefore is unstable and has poor pitch control. The preferred embodiment of the present invention uses four propulsion units and a multirotor control method to resolve this issue. Secondly, the design presented in U.S. Pat. No. 2,478,847 requires a complex system of drive shafts to drive the propellers using a gas engine.
Therefore there is a need to provide a Vertical Takeoff and Landing (VTOL) aircraft executing hovering flight, forward flight, and transitioning between the two in a stable and efficient manner, having a holistic design including one or more wings along with two or more fan propulsion units attached to tilting propulsion unit supports which allow for the tilting of all propulsion units for the production of thrust between a general vertical and general forward direction, where all said tilting fan propulsion units are strategically placed in a pusher configuration to maximize effective thrust by limiting or preventing the fan propulsion unit slipstream from hitting the wings, the tilting propulsion unit support, or any other part of the aircraft at any tilt angle.